Irritable bowel syndrome (IBS) is the most prevalent functional gastrointestinal disorder in western societies and recent research has proposed gut microbiota as one of the potential main factors involved. However, little is known regarding the relationship between the composition and function of the gut microbiota and clinical symptoms of IBS.

A recent study, led by Prof. Magnus Simrén from the Department of Internal Medicine & Clinical Nutrition and University of Gothenburg Centre for Person-Centered Care at the University of Gothenburg in Gothenburg (Sweden), has identified a gut microbiota profile that is related to the severity of IBS symptoms.

The researchers collected faecal and mucosal samples from adult Swedish normal-weight patients (aged 18-65 years) who met the Rome III criteria for IBS as well as from healthy subjects. The exploratory set comprised 149 subjects (110 with IBS and 39 healthy subjects); 232 faecal samples and 59 mucosal biopsy samples were collected and analysed by 16S ribosomal ribonucleic acid (rRNA) targeted pyrosequencing. The validation set comprised 46 subjects (29 with IBS and 17 healthy subjects); 46 faecal samples (but no mucosal samples) were collected and analysed. Besides this, exhaled hydrogen (H2) and methane (CH4), oro-anal transit time, and severity of psychological and gastrointestinal symptoms were measured for each subject.

Paired mucosal and faecal microbiota sample analysis in the exploratory set of patients revealed that faecal and mucosal microbiota were structurally distinct but highly correlated. Although there were no differences in faecal microbiota composition between patients with IBS when compared to healthy subjects, a computational statistical procedure identified a microbial signature for severe IBS within the IBS group, consisting of 90 bacterial operational taxonomic units (OTUs), which are the most commonly used microbial diversity units clustered on the basis of deoxyribonucleic acid (DNA) sequence identity alone. The signature could not be explained by differences in diet or use of medications. This microbial signature allowed discrimination between patients with severe symptoms, patients with moderate/mild symptoms, and healthy subjects. Its robustness was confirmed in the validation set.

IBS symptom severity was associated with a distinct faecal microbiota signature that was also detected in the intestinal mucosa. This microbial signature was correlated with microbial richness, exhaled CH4, presence of faecal methanogens, enterotype stratification, stool consistency and transit time. In particular, the microbial signature for IBS severity was associated with low microbial richness, low CH4 exhaled, Bacteroides enterotypes enriched and absence of Methanobacteriales.

In conclusion, IBS symptom severity may be associated with a distinct faecal microbiota signature. Although this microbial signature cannot be used as a predictor of IBS clinical severity yet, it provides new information in identifying links between gut microbiota and clinical features.

Andreu PradosAndreu Prados holds a Bachelor of Science Degree in Pharmacy & Human Nutrition and Dietetics. Science writer specialised in gut microbiota and probiotics, working also as lecturer and consultant in nutrition and healthcare. Follow Andreu on Twitter @andreuprados

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Gut Microbiota for Health has been created by the Gut Microbiota and Health Section of the European Society for Neurogastroenterology & Motility (ESNM), member of United European Gastroenterology (UEG)